Protease-activated receptor (PAR) is a type of trimeric G protein-coupled seven-transmembrane receptors and belongs to the receptor family mediating the cell action of serine proteases, and four molecules, PAR1, PAR2, PAR3 and PAR4, have been cloned so far.
Serine proteases cleave an extracellular amino-terminal peptide chain of the PAR molecule at a specific site and thus expose a new amino-terminal peptide chain having a receptor activation sequence consisting of 5 or 6 amino acid residues. The newly exposed amino-terminal peptide chain cleaved by a serine protease bonds as a chain-like ligand to the extracellular loop 2, which is the active site of PAR2 itself and thus activates PAR2. PAR2 is known to be activated by trypsin, tryptase, kallikrein (mainly kallikreins 2, 4, 5, 6 and 14), blood coagulation factor VIIa, blood coagulation factor Xa, and the like, and also activated when a synthetic peptide consisting of 5 or 6 amino acids synthesized based on the receptor activation sequence enters exogenously (see Non Patent Literatures 1 to 3).
PAR2 herein is widely distributed in vivo such as blood vessel, prostate gland, small intestine, large intestine, liver, kidney, pancreas, stomach, lung, brain and skin, and known to be an aggravating factor in various diseases such as neurogenic inflammation, pain, itch, inflammation and allergy (see Patent Literatures 1 and 2, and Non Patent Literatures 4 to 6). For this reason, a PAR2 inhibitor is expected to be a possible treatment drug for these diseases and suggested to be, for example, a treatment drug for inflammatory bowel diseases, a treatment drug for dermatitis, a treatment drug for allergic diseases, or a preventive drug for skin pigmentation (see Patent Literatures 3 to 5 and Non Patent Literatures 3 and 6 to 11).